The GRAAL (Gamma-Ray Astronomy at ALmeria) project is presently using the CESA-I heliostat field at the Plataforma Solar de Almeria (PSA) as a gamma-ray telescope with an energy threshold of around 250 GeV.  CESA-I consists of 300 heliostats with a mirror size of 39.7 m2 each which reflect the Sun light onto a central tower. During the night, 63 heliostats direct the Cherenkov light generated by air-showers arriving in the direction of the cosmic source, through four non-imaging light concentrators housed in a special enclosure in the tower  which collect the Cherenkov light into a large-area PMT each. The incoming Cherenkov light consists of a train of pulses each one coming from a different heliostat. The arrival time and amplitude of the pulses is measured by using fast electronics.


Figure 1a):  The CESA-I heliostat field at the Plataforma Solar de Almeria during the day.



Figure 1b):  CESA-I is used at night for the detection of the Cherenkov light produced by extensive air showers generated by cosmic gamma-rays (artistic view).

The GRAAL project is a collaboration of the following institutions:

Other collaborators:


Last revised July 2001/May 2018